Understanding the role of andesite igneous rock in enhancing the performance of alkali-activated ultrafine slag exposed to normal and elevated temperatures

According to the literature, the engineering properties of alkali-activated slag (AAS) generally decrease as temperatures rise up to 1200 degrees C. Although the addition of certain amorphous aluminosilicate additives can in-crease the residual strength of AAS, it still exhibits lower performance compared to samples cured at ambient temperature. Hence, there is a significant need to identify an effective additive that can greatly enhance the thermal stability of AAS at elevated temperatures. In this study, the contribution of andesite igneous rock (AIR) in improving the performance of alkali-activated ultrafine slag (AAUS) at normal and elevated temperatures was evaluated. The addition of AIR at a weight percentage of 10 % enhances the performance of humidity-cured AAUS through its filling and nucleating effect. However, increasing the AIR content beyond 90 wt% nega-tively impacts the physical and mechanical performance of AAS due to the low reactivity of AIR towards alkali activation. Nevertheless, higher AIR content enhances the tolerance capacity of AAUS to temperatures as high as 1200 degrees C. AIR acts as a microaggregate in the activated system, reducing the contraction of AAUS at temperatures below 1000 degrees C. At higher temperatures, the unreacted AIR undergoes transformation into solidified melt and thermally-stable pyroxenes. This results in microstructural compaction and an increase in compressive strength, particularly when the AIR content exceeds 50 wt%.